Heat exchanger



FIG. 1 is a perspective view of the heat exchanger;

FIG. 2 is a front view thereof;

FIG. 3 is a rear view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a right side view thereof;

FIG. 6 is top view thereof; and,

FIG. 7 is a bottom view thereof.

The broken away symbols in the drawings indicate that any portion of the article beyond what is shown forms no part of the claimed design. The broken lines shown in the drawings are for the purpose of illustrating portions of the article that form no part of the claimed design. 

CLAIM The ornamental design for a heat exchanger, as shown and described. 